| CLINICAL BIOCHEMISTRY DEPARTMENT |
|
ORAL LACTOSE TOLERANCE TEST
INTRODUCTION
This test is used in the investigation of suspected lactose intolerance. It is rarely performed, as it frequently results in diarrhoea and abdominal pain in affected individuals and has largely been superseded by the assay of lactase in a small bowel biopsy.
PRINCIPLE
Lactase deficiency in the small intestine leads to lactose intolerance and consequent failure of the blood glucose to rise normally following ingestion of lactose-containing products, particularly milk.
PRECAUTIONS
Please refer to the Trust’s phlebotomy procedure for sample collection precautions.
This test should not be carried out on patients with glucose intolerance (including diabetes), since results cannot be interpreted.
PATIENT PREPARATION
This test should be performed in the morning after at least three days of unrestricted diet (greater than 150 g of carbohydrate daily) and usual physical activity. The test should be preceded by an overnight fast of 10-16 hours, during which water may be drunk. Smoking is not permitted during the test.
Lactose load: |
50g of lactose dissolved in 300ml of water. |
Children: 1.0 g of lactose per kg body weight up to a maximum of 50g. |
PROTOCOL
| 1. | Take fasting blood sample for glucose (minimum 1ml into fluoride tube – grey top). |
| 2. | Give the appropriate lactose load (see above) orally over a period of 5 minutes. Care should be taken to avoid vomiting. Timing of the test is from the beginning of the drink. |
| 3. | Take further blood samples for glucose (minimum 1ml into fluoride tube – grey top) at 30, 60, 90 and 120 minutes after lactose ingestion. |
| 4. | Please note any gastrointestinal symptoms such as: nausea, rumbling, abdominal pain or diarrhoea suffered by the patient during the test. |
INTERPRETATION
Lactase deficiency, whether primary (congenital) or secondary, is confirmed by a failure of plasma glucose to rise by at least 1.0 mmol/L and the spontaneous complaint of gastrointestinal symptoms.
Failure of glucose to rise adequately may also be due to non-compliance by the patient, vomiting of the test dose or delayed gastric emptying.
Reviewed by: Tony
Everitt, Consultant Biochemist
Last edited 07/08/08